1. Field of the Invention
The present invention relates to a method of controlling ammonia amount absorbed in a selective catalytic reduction catalyst and an exhaust system using the same. More particularly, the present invention relates to a method of controlling ammonia amount adsorbed in a selective catalytic reduction (SCR) catalyst and an exhaust system using the same that improves performance of the SCR catalyst by adsorbing more ammonia (NH3) in the SCR catalyst while preventing slip of the NH3 from the SCR catalyst.
2. Description of Related Art
Generally, exhaust gas flowing out from an engine through an exhaust manifold is urged into a catalytic converter mounted at an exhaust pipe and is purified therein. After that, the noise of the exhaust gas is decreased while passing through a muffler and the exhaust gas is then emitted into the air through a tail pipe. The catalytic converter purifies pollutants contained in the exhaust gas. In addition, a particulate filter for trapping particulate matter (PM) contained in the exhaust gas is mounted in the exhaust pipe.
A selective catalytic reduction (SCR) catalyst is one type of such a catalytic converter.
Reducing agent such as urea, ammonia, carbon monoxide and hydrocarbon (HC) reacts better with nitrogen oxide than with oxygen in the SCR catalyst.
An exhaust system of a vehicle provided with the SCR catalyst includes an urea tank and dosing module. The dosing module injects reducing agent such as urea into the exhaust gas passing through the exhaust pipe, and thereby the SCR catalyst purifies the nitrogen oxide efficiently.
The reducing agent injected from the dosing module is adsorbed in the SCR catalyst, is released if the exhaust gas containing the nitrogen oxide passes through the SCR catalyst, and reacts with the nitrogen oxide.
However, amount of the reducing agent adsorbed in the SCR catalyst is closely related to temperature of the SCR catalyst. Therefore, if the amount of the reducing agent more than maximum amount of the reducing agent that can be adsorbed in current temperature of the SCR catalyst is adsorbed in the SCR catalyst, a portion of the reducing agent is slipped from the SCR catalyst.
Ammonia is typically used as the reducing agent of the SCR catalyst. If the ammonia is slipped from the SCR catalyst, the slipped ammonia may cause stink and customers may have complaints. Therefore, it is very important to prevent the reducing agent from being slipped from the SCR catalyst.
According to a conventional method of controlling NH3 amount adsorbed in the SCR catalyst, the SCR catalyst is controlled to adsorb NH3 amount obtained by dividing maximum NH3 amount at the current temperature of the SCR catalyst by a substantially large safety factor. That is, the SCR catalyst is controlled to adsorb the NH3 amount that is smaller than the maximum NH3 amount so as to prevent slip of the NH3 from the SCR catalyst. Therefore, the SCR catalyst may underperform.
In addition, since the SCR catalyst underperforms, volume of the SCR catalyst should be increased.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.